1. Field of the Invention
This invention pertains, in general, to the field of retractable covers or roofs for large structures, such as athletic stadiums. More specifically, the invention relates to an improved transport mechanism for such a structure that is more compact, reliable, stable, mechanically simple and inexpensive to construct than comparable mechanisms heretofore known.
2. Description of the Related Technology
It is common these days for athletic stadiums to be constructed with retractable roofs, because this type of construction offers spectators the pleasure of being outdoors on nice days, while providing shelter when necessary against extreme temperatures and inclement weather conditions.
A number of factors must be taken into account in the design of a stadium that has a retractable roof. For instance, the forces created by the exertion of natural forces such as wind, rain snow and even earthquakes on such a large structure can be enormous, and the roof, the underlying stadium structure and the transport mechanism that is used to guide and move the roof between its retracted and operational positions must be engineered to withstand the worst possible confluence of such forces. In addition, for reasons that are both aesthetic and practical, it is desirable to make the structural elements of the roof and the transport mechanism to be as unobtrusive and as space-efficient as possible. It is desirable to make the roof structure and the transport mechanism to be as simple and maintenance-free as possible, and to be constructed so as to be able to open and close as quickly as possible.
Many cities in the United States and elsewhere are now using or building retractable roofed stadiums. The designs of the various stadiums are quite different, but there are a number of deficiencies that seem to be common to all of the designs that have been implemented thus far. For example, the transport mechanisms in most of the stadiums tend to be quite large, being as much as twenty to thirty feet in height. The transport mechanisms further tend to include a relatively small number of very large, heavily loaded wheels and bearings, and a small number of very large motors or actuators to drive the roof between the retracted and operational positions. The small number of large wheels exert very large concentrated loads onto the support structure, which requires the support structure to be heavily reinforced, adding to the cost and complexity of the stadium as a whole. The roof and transport mechanisms in existing designs further tend to be relatively heavy and inflexible, and often experience alignment problems during movement.
A need exists for an improved design for a stadium that has a retractable roof that is more compact, reliable, stable, mechanically simple and inexpensive to construct than comparable mechanisms heretofore known.